LED Driver Using Phase-Shifted PWM Signals
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Solution Overview
Problem
Existing LED light source drivers face challenges in controlling light intensity effectively at low duty cycles, leading to perceivable flickering and inaccurate light level control due to limitations in PWM frequency and power converter switching frequencies.
Innovation Solution
A driver apparatus that uses two or more separate output currents with synchronized control signals in predetermined time offsets to drive a single array of light emitting diodes, allowing for precise control of light intensity by deriving and setting duty cycles using a predefined mapping function, thereby increasing the effective PWM cycle frequency without introducing flicker or accuracy issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low PWM frequency is used, then power converter switching losses are reduced, but perceivable flickering occurs at low duty cycles
Solution Approach 1:
The patent applies periodic action by using multiple PWM signals with different phases (e.g., 0°, 120°, 240°) to periodically drive the LED array. This multi-phase periodic approach ensures that when one PWM signal is in its off period, other signals are in their on periods, thereby maintaining continuous light output and eliminating flickering while allowing each individual PWM signal to operate at lower frequencies that reduce switching losses.
2Object-affected harmful factors
If high PWM frequency is used, then flickering is eliminated, but inaccurate light intensity control occurs due to power converter switching operation
Solution Approach 1:
The patent uses multiple PWM signals with different phases to create a combined periodic driving effect. By distributing the duty cycles across multiple phases (e.g., setting duty cycles such that their sum equals the desired overall duty cycle), the system achieves accurate light intensity control while maintaining high effective frequency to eliminate flickering. The phase distribution allows precise control of the average current through the LED array.
3Device complexity
If single PWM signal is used, then device complexity is reduced, but both flickering and inaccurate light control cannot be simultaneously avoided
Solution Approach 1:
The patent segments the single PWM control signal into multiple phase-shifted PWM signals (e.g., three phases with 120° separation). Each phase signal drives a portion of the LED array or is combined through current summation. This segmentation allows each individual PWM signal to operate at relaxed frequencies while the combined effect provides continuous, stable light output with accurate intensity control, thereby improving reliability without excessive complexity.
Solution Approach 2:
By implementing multiple periodic PWM signals with different phases, the system achieves more reliable light output control. The periodic nature of each phase signal, when combined, ensures continuous illumination and accurate duty cycle control, overcoming the limitations of a single PWM signal approach.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the LED array to be driven at higher effective cycle frequencies while maintaining accurate light intensity control, reducing flicker and improving the reliability of light output, even at low duty cycles.
Implementation Method 1
A driver for a light emitting diode (LED) light source may apply a control signal
Data Source
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AI summary
A driver apparatus for driving one or more light emitting diodes is provided. The apparatus comprises one or more power source portions for providing two or more driving currents and a control portion for issuing two or more control signals for controlling the provision of two or more driving currents, each control signal exhibiting a respective duty cycle at a first cycle frequency, wherein the control portion is configured to issue the two or more control signals as synchronized control signals in predetermined time offsets with respect to each other for provision of the two or more driving currents in different phases.